The Night Sky This Month

The Planets

Mercury

From mid-northern latitudes look for Mercury during June's first week, very low in the west 30 minutes after sunset. The innermost planet shines at magnitude +1.4 and through a telescope shows a 10 arcseconds-diameter disk that is 20-percent illuminated. As the days pass, Mercury fades and sinks toward the horizon, reaching inferior conjunction with the Sun on June 19.

The first telescopic observations of Mercury were made by Galileo

in 1610, and although he observed phases when he looked at Venus, his telescope was not powerful enough to see the phases of Mercury. Three decades later Giovanni Zupi, an Italian astronomer, mathematician, and Jesuit priest, peered at Mercury through a more powerful telescope than the one used by Galileo and discovered that the planet went through phases like the Moon.

These observations were easily explained by understanding that the two planets orbited between Earth and the Sun, and were profoundly significant because they were proof that the Copernican theory was correct and the Earth was not the center of the Universe.

Except for the discovery of the phases of Mercury, early observations did not contribute much to our understanding of the planet. Most of our detailed knowledge has been obtained from one probe, Mariner 10. It was launched on November 3, 1973, and during three flybys of Mercury, it photographed more than half of the planet's moonlike surface.

Venus

At magnitude -4 Venus is the brightest morning "star", but it is not high above the horizon. Look for it blazing low in the east right around the first light of dawn. To get a steady view of the 80-percent-lit planet in a telescope, try following it until sunrise or even later.

One of the handful of planets known to the ancients, Venus is often called Earth's sister planet because of its similar size and distance from the Sun. Despite these similarities, however, in other ways Venus is very much unlike Earth. The planet is so hot and forbidding that it might be a good place to film Dante's Inferno.

The Earth's atmosphere consists of nearly 80-percent nitrogen and 20-percent oxygen, with small amounts of water, carbon dioxide, and ozone. Venus, on the other hand, has an atmosphere made up of about 96-percent carbon dioxide, 3.5-percent

nitrogen, and small amounts of water and sulfuric acid - the same acid used in car batteries.

In fact, the clouds we see on Venus are made up in large part of sulfuric acid droplets. Chemical reactions between the sulfuric acid in the atmosphere and other elements in the surface rocks result in some very corrosive substances that can dissolve even lead. The planet is indeed inhospitable.

Mars

This image of Mars taken by the Vikingorbiter in 1980 shows the large, darkexpanse of the extinct shield volcano SyrtisMajor. The streaks are windblown dust.USGS Astrogeology Science Center[larger image]

Mars pops into view due south as twilight deepens at the beginning of June, but it is well past the meridian at sunset by the end of the month. On June 1, Mars glows brightly at magnitude -0.5, some four times brighter than its 1st-magnitude neighbor, Spica. By June 30, the planet has faded to +0, matching Arcturus and Vega.

The Red Planet reached opposition and peak visibility in April, so the distance between it and Earth grows steadily this month. Seen in a telescope, Mars is 11 arcseconds wide around mid-June. At moderately high magnification it appears as a small, distinct reddish ball displaying subtle dark markings and a bright white North Polar Cap. The red color comes from rust - iron oxide - that makes up about 10-percent of Martian soil. It is thought the oxide was created far back in the planet's history, when surface water was abundant and reacted with iron in the rocks on Mars' surface.

As Viking 1 and Mars Pathfinder images revealed, even the Martian sky takes on a rust-pink tinge during seasonal dust storms. The dust is blown from the surface by winds with speeds exceeding 150 to 300 feet (45 to 90 meters) per second, and forced into the atmosphere, where it remains suspended for weeks. Widespread dust storms are commonest when Mars is near perihelion (the point in its orbit when it is nearest to the Sun), and the surface winds are at their strongest.

Jupiter

Viewing the giant of the solar system canbe more than fun - even with a modesttelescope you can easily see the cloud bandsand Jupiter's largest moons. NASA/ESA[larger image]

The solar system's largest planet glares in the west during evening, among the background stars of Gemini, a bright constellation of the zodiac located between Taurus to the west and Cancer to the east. You will not need any help spotting Jupiter; at magnitude -1.8 it is the brightest point of light in the sky and stands out on any clear evening.

Jupiter is the King of the Planets, and not just because of its enormous size - this monster planet is 88,700 miles (142,700 kilometers) in diameter. Jupiter also reigns over the other members of the solar system in the affections of amateur astronomers, because this great ball of gas is just so consistently interesting.

There is always a tremendous variety of interesting phenomena

to see when Jupiter is in the sky. The planet shows detail in small telescopes and even the smallest optical aid will show its four bright moons. In backyard telescopes, you can make out two or three of the darkest cloud bands and as the scope gets bigger, the more you will see.

6-inch telescopes can show multiple bands and the Great Red Spot. Larger scopes can see details in the bands such as texture, loops, and ovals, often in vivid color. Also visible in larger scopes are transits of the moons across Jupiter's surface as well as the inky black dots of the moons' shadows as they transit the planet's disk.

Saturn

This NASA picture taken on January 19, 2007, shows aview of Saturn and its rings. The rings are made up ofbillions of ice particles, thought to be pieces of cometsor shattered moons. NASA/JPL [larger image]

The ringed planet reached opposition and peak visibility in May, but remains a stunning sight through any telescope during June. It shines high in the southeast, among the stars of Libra the Balance and midway between Spica and Antares, about half an hour after sundown.

At the beginning of June, Saturn is magnitude +0.2 and its globe is 19 arcseconds wide. By late in the month, the disk has shrunk to 18 arcseconds and the planet also glows slightly dimmer, at magnitude +0.4. The rings span 42 arcseconds, more than double the planet's disk,

and tilt 21° to our line of sight. You should have no trouble spotting the Cassini Division, a thin black gap in the rings named in honor of Giovanni Domenico Cassini, who discovered it in 1675.

Saturn's rings are one of the spectacles of the night sky when seen through a decent telescope. When Galileo trained a primitive telescope on the planet for the first time in 1610, he was misled. From the poorly resolved image in his viewfinder, he believed Saturn to be a triple-system, with a large body in the center and smaller ones on each side.

The rings may be much younger than the planet itself, and great mathematicians have found them worthy of contemplation. Laplace and James Clerk Maxwell calculated that Saturn's rings must consist of many smaller objects, all moving round the planet in the manner of tiny moons. There is no mystery about their composition; they are made up of ordinary water ice.

Uranus

Uranus stands about 10° above the eastern horizon shortly before morning twilight begins. Glowing at magnitude +5.9 it pops into view in binoculars, even from moderately light-polluted sites. Look for it in Pisces the Fish, nearly due south of Epsilon Piscium and southeast of Delta Piscium.

The planet moves eastward relative to the background stars during the month. Through a telescope, Uranus displays a disk 3.4 arcseconds in diameter sporting a distinct blue-green hue. The color is caused by methane in the Uranian atmosphere; methane absorbs light at red wavelengths and leaves blue-green as the dominant hue.

Uranus was discovered on March 13, 1781, by German-born British astronomer William Herschel, using a 6.2-inch reflector with a magnification of 227x. Herschel realized that the object - at that time in the constellation Gemini - was not a star, but he believed it to be a comet, and indeed his communication to the Royal Society was headed "An Account of a Comet".

There was prolonged debate over the naming of the new planet. J. E. Bode suggested Uranus, after the first ruler of Olympus. Other names were proposed - for example Hypercronius and "The Georgian Planet", by Herschel himself in honor of his patron, King George III. It was not until 1850 that the name "Uranus" became universally accepted.

Neptune

Dark, cold and whipped by supersonic winds,Neptune is the last of the hydrogen and heliumgas giants in our solar system. NASA/JPL[larger image]

Seek out Neptune just before dawn, in central Aquarius, 2° northeast of the 5th-magnitude star Sigma Aquarii. The planet lies 2.8 billion miles (4.5 billion kilometers) from Earth and glows dimly at magnitude +7.9. A 4-inch diameter telescope is probably the minimum required to see the planet and resolve its disk, only 2.5 arcseconds across.

Neptune is a cold, dark world. With a mean solar distance of 30.11 astronomical units, light levels at Neptune are more than 800 times dimmer than they are on Earth. Noon on Neptune would appear no brighter than what a human would experience at dusk on Earth. Even the Sun would take on an appearance more like a star than the bright disk seen from our home planet.

Because Neptune is so distant, so far

only one spacecraft, Voyager 2, has visited the planet - a flyby in 1989. The spacecraft observed Neptune almost continuously between June and October of that year. It measured the planet's radius and interior rotation rate, confirmed that Neptune has rings, and discovered six new moons. Voyager 2 also recorded pulses of radio emission, zonal cloud bands, and large-scale storm systems with up to 1,500 miles (2,400 kilometers) per hour winds - the strongest measured on any planet.

Pluto

Clyde Tombaugh, the Americanastronomer best known fordiscovering the dwarf planet Plutoin 1930, at his family farm inKansas. Tombaugh had been agifted telescope builder - over thecourse of his life, he built more than30 instruments. ASD/NASA/GSFC[larger image]

The dwarf planet Pluto was discovered in 1930 as a result of an extensive search by American astronomer Clyde Tombaugh. He used a blink comparator to reveal the motion of any planet relative to the background stars on pairs of photographic plates taken a few nights apart. On plates taken on January 23 and January 29, Tombaugh found a faint object which was moving by the amount expected of a trans Neptunian planet. The newly discovered object was named Pluto, after the ancient Greek god of the underworld.

Pluto drifts among the stars of the constellation Sagittarius and can be attempted with a fairly large telescope in the wee morning hours. A 10-inch instrument should catch the dwarf planet's 0.1 arcsecond disk, shining at magnitude +14. Because Pluto looks just like millions of similarly faint stars, identifying it is an exercise in precision map work at the telescope.

The two finder maps below will help you identify Pluto. First, locate its general position on the coarse finder map, and after you have identified the 7th-magnitude guide star HD 174383 use the fine finder map that shows the position of the dwarf planet on each night of the month.

The Deep Sky

Globular star clusters have always been the delight of amateur and professional astronomers alike. These wondrous swarms of ancient stars are impressive sights in almost any telescope. Because globulars are more numerous in the direction of the Milky Way's center, located towards Sagittarius and Scorpius, summer nights are the best time for globular hunting. Let us pay a visit to one!

The huge, loose cluster M4 is only 1.3° west of brilliant Antares, the fiery orange heart of the Scorpion. The "M" stands for Charles Messier, and anything that made this 18th-century observer's list is an easy target for newcomers to astronomy. All the telescopes Messier used were quite small; not even one had as much light grasp as a good 4-inch telescope of today.

Such an instrument at 70x will show many of M4's individual stars, some of which seem to be arranged in a central bar that runs nearly north-south. This feature is most prominent in an 8-inch telescope, and in larger instruments, it appears enmeshed in a multitude of fainter stars. As with almost any globular cluster, the longer one stares, the more patterns seem to emerge.

At nearly 7,000 light years away, M4 is considered by some authorities to be the closest globular cluster to Earth. (Others believe that NGC 6397 in Ara is slightly closer.) At this distance, the cluster's apparent size of 26 arcminutes corresponds to a diameter of about 40 light years. M4 lies toward the Galactic center, within roughly 2,000 light years of the Galactic central plane, so that interstellar material in the disk of our Galaxy blocks out some of its light and makes it dimmer (by a few magnitudes) than it would otherwise appear.

Astronomers classify M4 as a loose globular cluster of class IX. Globulars fall into classifications designated I to XII. A globular with a classification of I has the highest stellar density at its core. XII represents a homogenous globular with no increase in star concentration toward the center.

Asteroids

These Hubble Space Telescope images of Ceres (left) andVesta (right) show two of the most massive asteroids in themain-belt, a region between Mars and Jupiter.NASA/ESA/STScI [larger image]

This summer, the two brightest and most massive asteroids in the belt between Mars and Jupiter appear closer to each other than at any time since they were discovered, almost two hundred years ago. Ceres and Vesta loop nearly in parallel across the constellation Virgo, and show up easily in the same telescopic field of view.

At the start of June,

they lie some 2° apart and appear halfway up in the south after darkness falls. Vesta, the brightest member of the pair, is just below the naked eye barrier. At magnitude +8, Ceres is well out of naked eye range, but shows up easily through small telescopes.

As the month progresses, the separation between Ceres and Vesta will tighten considerably. The 2° gap in early June will dwindle to 1.3° on June 15 and 0.4° on June 30. Then, on the North American evening of July 5, the two asteroids will appear only 10 arcminutes apart (one-third the Full Moon's diameter). However, this closeness is just an illusion; they will be at different distances, more than 40 million miles (65 million kilometers) from each other.

The close-up map below shows stars to magnitude +9, more than enough for identifying Ceres and Vesta in June. On the map north is up and east is left. When peering into the eyepiece, find north by nudging the telescope slightly towards Polaris - new stars enter the field from the north edge. Turn the map around and hold it so north on the map matches this direction.

Comets

C/2012 K1 PanSTARRS was discovered on May 19, 2012, using the PanSTARRS robotic telescope located near the summit of Haleakala, on the island of Maui in Hawaii. Glowing around 8th magnitude, this visitor from the outer solar system likely will appear similar in brightness and size to the brighter galaxies in the Messier catalog.

When June begins, PanSTARRS lies high in the evening sky among the background stars of Ursa Major, south of the widely recognized asterism known as the Big Dipper's bowl. The comet appears 4° east of 3rd-magnitude Mu Ursae Majoris on the 1st, and the gap closes to 2° about a week later.

As PanSTARRS dips southward, it crosses into Leo Minor, in a fairly barren region of the sky. Finally, by

month's end when the Moon's light no longer interferes with the view, the comet can be found above the sickle-shaped head of Leo the Lion. By then, C/2012 K1 PanSTARRS could be close to 7th magnitude, making it a binocular target for experienced observers.

C/2012 X1 LINEAR underwent a large outburst in mid-October 2013. Pictured above on April 8, the comet isstill bright and more than 20° high in the morning sky.Damian Peach [larger image]

Although never expected to become brighter than 14th-magnitude, in mid-October 2013 comet C/2012 X1 LINEAR suddenly brightened some 150 times to magnitude +8. Something similar happened with comet 17P/Holmes in 2007, when the "icy mud ball" brightened over half a million times from an uber-faint 17th-magnitude to a naked eye brightness of +2.8.

While cometary outbursts are common, their causes are unknown. One possibility is that a massive buildup of gas inside the comet

fractures and breaks off a large size of the crust, releasing a huge cloud of dust and gas. Another possibility is that outbursts are triggered by impacts with bodies that have sizes in the range of three or four feet (one meter).

Throughout all of June, C/2012 X1 should remain around 8th or 9th magnitude, making it an easy target for 6-inch telescopes. The comet cuts through the constellations Aquarius and Piscis Austrinus, which stand highest above the horizon in the predawn sky. The best views will come during the month's first and last weeks, when moonlight will not interfere with observing.

Use a range of magnifications to see all of the comet's features. If you bump up the power past 100x, you might even glimpse the "false nucleus", a pinprick shining in the middle of the brightest glow. The true surface of C/2012 X1 LINEAR lies hidden behind several bright layers of dust and gas, ejected in the previous several days.

Meteors

People spend a lot more leisure time outdoors during the summer months, so it is no wonder they observe more meteors at this time of the year. If you can survive the onslaught of hungry mosquitoes, a June evening can be a great time to view a few shooting stars blazing across the sky. The only equipment you will need is your eyes and a modest amount of patience.

The best meteor shower of June, in terms of both sky position and meteor activity, is the June Bootid stream. This well-known annual shower usually produces just a few visible meteors per hour, yet sixteen years ago, on June 27, 1998, northern sky watchers were surprised when dozens of bright meteors suddenly began to stream out of the constellation Bootes. It was not the first time: similar June Bootid outbursts had been recorded decades ago, in 1916, 1921, and 1927.

Several "shooting stars" or meteors per hourcan usually be seen on any given night. Around15,000 tones of meteoroids and different formsof space dust enter Earth's atmosphere eachyear. Yuichi Takasaka [larger image]

This year the June Bootids reach a peak on June 27, and can be seen from about June 22 through until July 2. The shower's radiant - the point in the sky from which meteors appear to originate from - is located in northern Bootes, and will be excellently positioned as darkness falls. It will appear nearly overhead and will remain in view through the whole night.

This is great news, but will you see a large number of meteors coming from Bootes on Friday evening, June 27? Unfortunately, the answer is probably not; no outburst is expected this year. However, it is worth keeping an eye open. No one knows why the June Bootid shower spiked in 1998, or when it might again.

Keep in mind that members of this shower are extremely slow, with a speed of "only" 11 miles (18 kilometers) per second. Meteors coming from the same radiant in Bootes, but not traveling more slowly than most other meteors visible at that time, are not June Bootids.

Some meteors do not belong to any known shower. These are the sporadic meteors, caused by random bits of comet debris spread throughout the inner solar system. They appear randomly across the sky all year long.

In this month's night sky careful observers can expect around four sporadics per hour during the morning hours and two during the dark evening.

Observing Aids

Northern Hemisphere's Sky - This map portrays the sky as seen near 40° north latitude at 11 P.M. local daylight time in early June and 10 P.M. in late June.

Southern Hemisphere's Sky - This map is plotted for 35° south latitude. It shows the sky at 8 P.M. local time in early June and 7 P.M. in late June.

Visibility of the Planets - The table provides general information about the visibility of the planets during the current month.

Phases of the Moon - This Moon Phase Calendar shows the Moon's phase for every day in June.

Jupiter's Moons - The diagram shows the positions of Galilean satellites on each day in June at midnight.

Sky Events

June 1 - 3 A.M. EDT: Asteroid 4 Vesta is stationary.

June 3 - 12:25 A.M. EDT: The Moon is at apogee, the point in its orbit when it is farthest from Earth.

June 10 - 2 A.M. EDT: Neptune is stationary. 3 P.M. EDT: The Moon is 0.6° south of Saturn.

June 13 - 12:11 A.M. EDT: Full Moon.

June 14 - 11:29 P.M. EDT: The Moon is at perigee, the point in its orbit when it is nearest to Earth.

June 18 - 6 A.M. EDT: The Moon is 5° north of Neptune.

June 19 - 2:39 P.M. EDT: Last Quarter Moon. 7 P.M. EDT: Mercury is in inferior conjunction with the Sun.

June 20 - 11 P.M. EDT: The Moon is 1.6° north of Uranus.

June 21 - 6:51 A.M. EDT: The June solstice occurs.

June 24 - 5 A.M. EDT: Asteroid 29 Amphitrite is at opposition. 9 A.M. EDT: The Moon is 1.3° south of Venus.

June 27 - 4:08 A.M. EDT: New Moon. 5 A.M. EDT: The June Bootid meteor shower is at peak activity.

June 28 - 11 P.M. EDT: The Moon is 5° south of Jupiter.

June 30 - 3:10 P.M. EDT: The Moon is at apogee, the point in its orbit when it is farthest from Earth.

The information provided on this page is accurate for the world's mid-northern latitudes. Finder maps for the five naked eye planets are plotted for 40° north latitude, but can also be used from other latitudes close to 40° north. Except the two all-sky maps, all other maps can be used no matter the latitude. Local time (local daylight time during summer) represents the time of the reader.